Low papr reference signal

ABSTRACT

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE receives an indication for transmitting a particular DMRS sequence in an uplink transmission. The particular DMRS sequence is time domain based. The UE generates the particular DMRS sequence. The UE modulates the particular DMRS sequence to obtain a set of symbols. The UE maps a plurality of symbols of the set of symbols to a plurality of subcarriers. The UE transmits the plurality of symbols on the plurality of subcarriers.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefits of U.S. Provisional Application Ser. No. 62/791,116, entitled “LOW PAPR REFERENCE SIGNAL FOR π/2-BPSK DFT-S-OFDM” and filed on Jan. 11, 2019; U.S. Provisional Application Ser. No. 62/801,637, entitled “LOW PAPR REFERENCE SIGNAL FOR DFT-S-OFDM” and filed on Feb. 5, 2019; U.S. Provisional Application Ser. No. 62/806,016, entitled “LOW PAPR REFERENCE SIGNAL FOR π/2-BPSK DFT-S-OFDM” and filed on Feb. 15, 2019; U.S. Provisional Application Ser. No. 62/817,663, entitled “UE MULTIPLEXING FOR π/2-BPSK DMRS TRANSMISSION” and filed on Mar. 13, 2019; all of which are expressly incorporated by reference herein in their entirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, and more particularly, to techniques of selecting and transmitting demodulation reference signals (DMRSs) in an uplink transmission.

Background

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE receives an indication for transmitting a particular demodulation reference signal (DMRS) sequence in an uplink transmission. The particular DMRS sequence is time domain based. The UE generates the particular DMRS sequence. The UE modulates the particular DMRS sequence to obtain a set of symbols. The UE maps a plurality of symbols of the set of symbols to a plurality of subcarriers. The UE transmits the plurality of symbols on the plurality of subcarriers.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIG. 2 is a diagram illustrating a base station in communication with a UE in an access network.

FIG. 3 illustrates an example logical architecture of a distributed access network.

FIG. 4 illustrates an example physical architecture of a distributed access network.

FIG. 5 is a diagram showing an example of a DL-centric subframe.

FIG. 6 is a diagram showing an example of an UL-centric subframe.

FIG. 7 is a diagram illustrating communications between a base station and UE.

FIG. 8 is a flow chart of a method (process) for generating and transmitting a DMRS sequence.

FIG. 9 is a conceptual data flow diagram illustrating the data flow between different components/means in an exemplary apparatus.

FIG. 10 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations 102, UEs 104, and a core network 160. The base stations 102 may include macro cells (high power cellular base station) and/or small cells (low power cellular base station). The macro cells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) interface with the core network 160 through backhaul links 132 (e.g., S1 interface). In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the core network 160) with each other over backhaul links 134 (e.g., X2 interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102′ may have a coverage area 110′ that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102/UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell).

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152/AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102′ may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequencies and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW/near mmW radio frequency band has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 184 with the UE 104 to compensate for the extremely high path loss and short range.

The core network 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the core network 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service (PSS), and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

The base station may also be referred to as a gNB, Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The base station 102 provides an access point to the core network 160 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a toaster, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, etc.). The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

FIG. 2 is a block diagram of a base station 210 in communication with a UE 250 in an access network. In the DL, IP packets from the core network 160 may be provided to a controller/processor 275. The controller/processor 275 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 275 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 216 and the receive (RX) processor 270 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 216 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 274 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 250. Each spatial stream may then be provided to a different antenna 220 via a separate transmitter 218TX. Each transmitter 218TX may modulate an RF carrier with a respective spatial stream for transmission.

At the UE 250, each receiver 254RX receives a signal through its respective antenna 252. Each receiver 254RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 256. The TX processor 268 and the RX processor 256 implement layer 1 functionality associated with various signal processing functions. The RX processor 256 may perform spatial processing on the information to recover any spatial streams destined for the UE 250. If multiple spatial streams are destined for the UE 250, they may be combined by the RX processor 256 into a single OFDM symbol stream. The RX processor 256 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 210. These soft decisions may be based on channel estimates computed by the channel estimator 258. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 210 on the physical channel. The data and control signals are then provided to the controller/processor 259, which implements layer 3 and layer 2 functionality.

The controller/processor 259 can be associated with a memory 260 that stores program codes and data. The memory 260 may be referred to as a computer-readable medium. In the UL, the controller/processor 259 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the core network 160. The controller/processor 259 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 210, the controller/processor 259 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 258 from a reference signal or feedback transmitted by the base station 210 may be used by the TX processor 268 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 268 may be provided to different antenna 252 via separate transmitters 254TX. Each transmitter 254TX may modulate an RF carrier with a respective spatial stream for transmission. The UL transmission is processed at the base station 210 in a manner similar to that described in connection with the receiver function at the UE 250. Each receiver 218RX receives a signal through its respective antenna 220. Each receiver 218RX recovers information modulated onto an RF carrier and provides the information to a RX processor 270.

The controller/processor 275 can be associated with a memory 276 that stores program codes and data. The memory 276 may be referred to as a computer-readable medium. In the UL, the controller/processor 275 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 250. IP packets from the controller/processor 275 may be provided to the core network 160. The controller/processor 275 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

New radio (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). NR may utilize OFDM with a cyclic prefix (CP) on the uplink and downlink and may include support for half-duplex operation using time division duplexing (TDD). NR may include Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHZ may be supported. In one example, NR resource blocks (RBs) may span 12 sub-carriers with a sub-carrier bandwidth of 60 kHz over a 0.125 ms duration or a bandwidth of 15 kHz over a 0.5 ms duration. Each radio frame may consist of 20 or 80 subframes (or NR slots) with a length of 10 ms. Each subframe may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect to FIGS. 5 and 6.

The NR RAN may include a central unit (CU) and distributed units (DUs). A NR BS (e.g., gNB, 5G Node B, Node B, transmission reception point (TRP), access point (AP)) may correspond to one or multiple BSs. NR cells can be configured as access cells (ACells) or data only cells (DCells). For example, the RAN (e.g., a central unit or distributed unit) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity and may not be used for initial access, cell selection/reselection, or handover. In some cases DCells may not transmit synchronization signals (SS) in some cases DCells may transmit SS. NR BSs may transmit downlink signals to UEs indicating the cell type. Based on the cell type indication, the UE may communicate with the NR BS. For example, the UE may determine NR BSs to consider for cell selection, access, handover, and/or measurement based on the indicated cell type.

FIG. 3 illustrates an example logical architecture 300 of a distributed RAN, according to aspects of the present disclosure. A 5G access node 306 may include an access node controller (ANC) 302. The ANC may be a central unit (CU) of the distributed RAN 300. The backhaul interface to the next generation core network (NG-CN) 304 may terminate at the ANC. The backhaul interface to neighboring next generation access nodes (NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs 308 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, or some other term). As described above, a TRP may be used interchangeably with “cell.”

The TRPs 308 may be a distributed unit (DU). The TRPs may be connected to one ANC (ANC 302) or more than one ANC (not illustrated). For example, for RAN sharing, radio as a service (RaaS), and service specific AND deployments, the TRP may be connected to more than one ANC. A TRP may include one or more antenna ports. The TRPs may be configured to individually (e.g., dynamic selection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture of the distributed RAN 300 may be used to illustrate fronthaul definition. The architecture may be defined that support fronthauling solutions across different deployment types. For example, the architecture may be based on transmit network capabilities (e.g., bandwidth, latency, and/or jitter). The architecture may share features and/or components with LTE. According to aspects, the next generation AN (NG-AN) 310 may support dual connectivity with NR. The NG-AN may share a common fronthaul for LTE and NR.

The architecture may enable cooperation between and among TRPs 308. For example, cooperation may be preset within a TRP and/or across TRPs via the ANC 302. According to aspects, no inter-TRP interface may be needed/present.

According to aspects, a dynamic configuration of split logical functions may be present within the architecture of the distributed RAN 300. The PDCP, RLC, MAC protocol may be adaptably placed at the ANC or TRP.

FIG. 4 illustrates an example physical architecture of a distributed RAN 400, according to aspects of the present disclosure. A centralized core network unit (C-CU) 402 may host core network functions. The C-CU may be centrally deployed. C-CU functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity. A centralized RAN unit (C-RU) 404 may host one or more ANC functions. Optionally, the C-RU may host core network functions locally. The C-RU may have distributed deployment. The C-RU may be closer to the network edge. A distributed unit (DU) 406 may host one or more TRPs. The DU may be located at edges of the network with radio frequency (RF) functionality.

FIG. 5 is a diagram 500 showing an example of a DL-centric subframe. The DL-centric subframe may include a control portion 502. The control portion 502 may exist in the initial or beginning portion of the DL-centric subframe. The control portion 502 may include various scheduling information and/or control information corresponding to various portions of the DL-centric subframe. In some configurations, the control portion 502 may be a physical DL control channel (PDCCH), as indicated in FIG. 5. The DL-centric subframe may also include a DL data portion 504. The DL data portion 504 may sometimes be referred to as the payload of the DL-centric subframe. The DL data portion 504 may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, the DL data portion 504 may be a physical DL shared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 506. The common UL portion 506 may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. The common UL portion 506 may include feedback information corresponding to various other portions of the DL-centric subframe. For example, the common UL portion 506 may include feedback information corresponding to the control portion 502. Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The common UL portion 506 may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information.

As illustrated in FIG. 5, the end of the DL data portion 504 may be separated in time from the beginning of the common UL portion 506. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 6 is a diagram 600 showing an example of an UL-centric subframe. The UL-centric subframe may include a control portion 602. The control portion 602 may exist in the initial or beginning portion of the UL-centric subframe. The control portion 602 in FIG. 6 may be similar to the control portion 502 described above with reference to FIG. 5. The UL-centric subframe may also include an UL data portion 604. The UL data portion 604 may sometimes be referred to as the pay load of the UL-centric subframe. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion 602 may be a physical DL control channel (PDCCH).

As illustrated in FIG. 6, the end of the control portion 602 may be separated in time from the beginning of the UL data portion 604. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). The UL-centric subframe may also include a common UL portion 606. The common UL portion 606 in FIG. 6 may be similar to the common UL portion 606 described above with reference to FIG. 6. The common UL portion 606 may additionally or alternatively include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE1) to another subordinate entity (e.g., UE2) without relaying that communication through the scheduling entity (e.g., UE or BS), even though the scheduling entity may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum).

FIG. 7 is a diagram 700 illustrating communications between a base station 702 and a UE 704. The base station 702 may send to the UE 704 an indication (e.g., via RRC signalings) indicating a particular time domain DMRS sequence 742. “DMRS” stands for Demodulation Reference Signal. Upon receiving the indication, the UE 704 instructs a DMRS sequence component 712 to generate the DMRS sequence 742. The DMRS sequence component 712 accordingly generates the DMRS sequence 742. The DMRS sequence component 712 sends the DMRS sequence 742 to the modulation component 714. The modulation component 714 generates modulation symbols 744 representing the DMRS sequence 742. The modulation component 714 then sends the modulation symbols 744 to a DFT-s-OFDM component 718. “DFT-s-OFDM” stands for Discrete Fourier Transmission-Single Carrier-Orthogonal Frequency Division Multiplexing.

More specifically, the DFT-s-OFDM component 718 includes a DFT component 722, an optional FDSS component 724, a tone mapper 726, an IFFT component 728, and a cyclic prefix component 730. “FDSS” stands for Frequency Domain Spectrum Shaping. “IFFT” stands for Inverse Fast Fourier Transform. The DFT component 722 performs a DFT on the modulation symbols 744. The outcome symbols from the DFT component 722 may be optionally sent to the FDSS component 724. The outcome symbols from the FDSS component 724 are then mapped to resource elements by the tone mapper 726. The resource elements carrying the symbols are converted to a time domain signal by the IFFT component 728. The cyclic prefix component 730 further adds a cyclic prefix to the time domain signal. As such, the UE 704 may transmit the DMRS sequence 742 to the base station 702 through a Physical Uplink Control Channel (PUCCH) or a Physical Uplink Shared Channel (PUSCH).

When the length of the DMRS sequence 742 is equal to or less than 24, the DMRS sequence 742 is selected from a set predetermined computer-generate-sequences (CGSs). In particular, the set may contain 30 base DMRS sequences. The set of predetermined CGSs may have desired properties such as good auto-correlation (within a delay window) or frequency flatness, good cross-correlation (between any pair of 30 base sequences), and good Peak-to-Average Power Ratio (PAPR).

When the length of the DMRS sequence 742 is 12, 18, or 24, the modulation component 714 may employ a π/2-BPSK modulation. When the length of the DMRS sequence 742 is 6, the modulation component 714 may employ an 8-BPSK modulation.

Two different types of DMRSs can be configured, namely, DMRS Type 1 and Type 2, which differ in the maximum number of orthogonal reference signals and the mapping to the resource elements in the frequency domain. Type 1 provides up to four orthogonal reference signals using a single-symbol DMRS and up to eight orthogonal reference signals using a double-symbol DMRS, whereas Type 2 provides 6 and 12 patterns for single and double-symbol DMRS, respectively.

DMRS type 1 supports total four ports in an OFDM symbol. Two of ports may share the same frequency domain locations (same code division multiplexing (CDM) group). It, therefore, relies on properties of the DMRS sequences to achieve orthogonality (or low correlation) between the ports. Table A below summaries UE multiplexing requirement for PUSCH, PUCCH format 3, and PUCCH format 4.

TABLE A PUCCH PUCCH PUSCH format 3 format 4 Sequence length 6, 12, 18, 24, >=30 12, 24, >=36 12 # of UE mux 2 N/A 4 (in same CDM group)

In Release 15, the orthogonality is assured by time domain cyclic shifts of a DMRS sequence that has constant amplitude in frequency domain. Furthermore, the shift values for each port are evenly distributed over the base sequence length, so in time domain two ports are orthogonal not only when they are fully aligned but also within a certain delay window. Note that the frequency pattern for the ports are [+, +, +, +, . . . ] and [+, −, +, −, +, −, . . . ] respectively for each port.

Given a time domain π/2-BPSK base sequence, two possible schemes may be used to multiplex two ports (i.e., a 1st port and a 2nd port). In Scheme 1, a time domain circular shift is applied to the 2nd port. For example, when the 1st port transmits the DMRS sequence 742, the 2nd port transmits a DMRS sequence that is formed by applying a time domain circular shift to the DMRS sequence 742. The DMRS sequence at the 2nd port can be formed by applying [+, −, +, −, +, −, . . . ] in frequency domain. With this approach, circular auto-correlation of the 2nd port may be as good as the 1st port but zero correlation between two ports (within a delay window) may not be retained in general. However, due to the property of Gold-sequence, the correlation can be still acceptable.

In Scheme 2: a time domain orthogonal mask can be applied to a base DMRS sequence at the 2nd port. Since pre-DFT time domain sequence has constant amplitude, we can apply a mask w=[w₀, w₁, . . . , w_(N-1)] (N is base sequence length) such that

Σ_(i=0) ^(N-1) w _(i)=0.

This can generate two DMRS sequences that are orthogonal when the two DMRS sequences are aligned. In order to maintain the same properties as π/2-BPSK, it is further restricted that w_(i)∈{1, −1} while the pattern of +1/−1 may be chosen. For example, w_(Blk)=[1, . . . , 1, −1, . . . , −1] may be considered as two equal sizes blocks of 1 and −1.

In another example, an interleaved pattern such as w_(intv)=[+1, −1, . . . , +1, −1] may be used. Applying w_(intv) is to circular shift (half of the length) in the frequency domain waveform. In other words, the 2nd port can be prepared in either time or frequency domain. Both ways have simpler implementations. When UE is in high speed environment, channel could change rapidly in time. Alternative interleaved +1 and −1, as w_(intv), may maintain orthogonality between ports better.

In certain configurations, CGS-based sequences having a length of 12, 18, or 24 bits are used for PUSCH with small RB allocations and CGS-based sequences having a length of 12 or 24 bits are also used in PUCCH format 3 and format 4.

In the case of PUSCH DMRS, two ports in the same CDM group are used. Both Scheme 1 and Scheme 2 can be considered as supporting two ports multiplexing. 30 CGS sequences of length 18 or 24 are searched to satisfy certain correlation properties, as described infra. One of the differences between two schemes is that Scheme 1 requires each base sequence itself has auto-correlation zeros for the window centered at 0 and the window centered at N/2.

For PUCCH format 3, no multiple user multiplexing is required. For PUCCH format 4, 4 users may need to be supported. Therefore, Scheme 1 and Scheme 2 are combined to form a Scheme 3 to support 2 additional ports.

In Scheme 3, a time domain circular shift of 6 bits and pre-DFT orthogonal masks are applied to a base DMRS sequence of a length 12. S_(i) is a base DMRS sequence. w_(intv)=[w^(i)], i=0, . . . , 11. The DMRS sequences at port 1, port 2, port 3, and port 4 are S_(i) ⁰, S_(i) ¹, S_(i) ², S_(i) ³ as follows

s _(i) ⁰ =s _(i),

s _(i) ¹ =s _(i) ·w _(i),

s _(i) ² =s _(mod(i+6,12)),

s _(i) ³ =s _(mod(i+6,12)) ·w _(i).

As such, for length 12, multiple DMRS sequences can be generated by Scheme 3 to support up to 4 UEs. For length 18 and length 24, two DMRS sequences may be generated by Scheme 1 and/or Scheme 2.

In certain configurations, for lengths supporting 2 ports (e.g., length 18 or 24), DMRS sequences generated for port 0 and port 1 (generated according to Scheme 1 or 2) both may have zero auto-correlation for delays in window T_(A). It searches sequences that minimizes the auto-correlation in T_(B) (if T_(B) is not empty) and minimizes cross-correlation in T_(A)∪T_(B)∪[0].

For the case supporting 4 ports (e.g., length 12), it is further restricted that the cross-correlation between any pair of the 4 ports are zero at delay=0. 30 such sequence may be identified as having good cross-correlation property in T_(A)∪T_(B)∪[0].

Table B below shows base sequences of length 12 generated based on Scheme 3.

TABLE B Index sequence PAPR 0 0 0 0 0 0 1 1 0 1 1 0 1 1.1896, 0.7793, 0.7794, 1.1900 1 0 0 0 0 1 1 0 1 1 0 1 0 1.2957, 1 7260, 1.7260, 1.2957 2 0 0 0 1 0 0 1 0 0 0 1 0 1.1900, 0.7794, 0.7793, 1.1896 3 0 0 1 0 1 1 1 0 1 1 1 0 1.2955, 1 7260, 1.7262, 1.2957 4 0 0 1 1 1 0 0 1 0 1 0 0 1.7260, 1.1900, 1.2957, 0.7793 5 0 0 1 1 1 1 1 0 1 0 0 1 1.1896, 0.7793, 0.7794, 1.1900 6 0 1 0 0 0 1 0 0 1 0 0 0 1.1896, 0.7794, 0.7794, 1.1896 7 0 1 0 0 0 1 1 1 0 1 0 0 1.1896, 0.7787, 0.7787, 1.1896 8 0 1 0 0 0 1 1 1 0 1 1 1 1.2957, 1.7262, 1.7260, 1.2955 9 0 1 0 1 1 0 0 0 1 1 1 1 1.2948, 1.7260, 1.7254, 1.2957 10 0 1 1 0 0 0 1 1 1 1 0 1 1.7260, 0.7787, 1.2957, 1.1896 11 0 1 1 0 1 0 0 0 0 0 1 1 1.2948, 1.7260, 1.7254, 1.2957 12 0 1 1 0 1 0 1 1 1 1 0 0 1.2948, 1.1896, 1.7254, 0.7787 13 0 1 1 1 0 0 1 0 1 0 0 0 1.7260, 1.7260, 1.2957, 1.2957 14 0 1 1 1 1 1 0 1 0 0 1 0 1.7254, 1.2948, 1.2948, 1.7254 15 1 0 0 0 0 0 1 1 0 1 1 0 1.1896, 0.7793, 0.7794, 1.1900 16 1 0 0 0 1 0 0 0 1 1 1 0 1.2957, 1.7260, 1.7260, 1.2957 17 1 0 0 0 1 0 1 1 1 0 0 0 1.1900, 0.7794, 0.7793, 1.1896 18 1 0 0 0 1 1 1 0 1 1 1 0 1.2955, 1.7260, 1.7262, 1.2957 19 1 0 0 1 0 0 0 0 1 0 0 0 1.7260, 1.1900, 1.2957, 0.7793 20 1 0 0 1 0 0 0 1 0 0 0 0 1.1896, 0.7793, 0.7794, 1.1900 21 1 0 1 1 0 0 0 0 0 1 0 1 1.1896, 0.7794, 0.7794, 1.1896 22 1 0 1 1 0 1 1 1 1 0 1 1 1.1896, 0.7787, 0.7787, 1.1896 23 1 0 1 1 1 0 0 0 1 0 1 1 1.2957, 1.7262, 1.7260, 1.2955 24 1 0 1 1 1 0 1 0 0 0 1 1 1.2948, 1.7260, 1.7254, 1.2957 25 1 0 1 1 1 1 0 0 0 1 1 0 1.7260, 0.7787, 1.2957, 1.1896 26 1 0 1 1 1 1 0 1 1 0 1 1 1.2948, 1.7260, 1.7254, 1.2957 27 1 1 0 1 0 0 0 1 0 0 0 1 1.2948, 1.1896, 1.7254, 0.7787 28 1 1 0 1 1 0 1 1 1 0 1 1 1.7260, 1.7260, 1.2957, 1.2957 29 1 1 0 1 1 1 0 1 1 1 1 0 1.7254, 1.2948, 1.2948, 1.7254

Table C below shows base sequences of length 18 generated based on Scheme 1.

TABLE C Index sequence PAPR 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 1 1 0 1.3798, 1.0231 1 0 0 0 0 1 1 1 0 0 0 1 1 1 0 1 1 1 0 0.9637, 1.3795 2 0 0 0 0 1 1 1 0 1 0 1 0 1 0 0 1 1 1 0.9646, 0.9907 3 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0 1.0239, 1.1808 4 0 0 0 1 0 1 0 1 0 1 1 0 0 0 1 1 1 1 1.0213, 1.0231 5 0 0 0 1 1 0 0 0 1 1 0 1 0 1 0 1 1 1 1.3056, 1.2438 6 0 0 0 1 1 1 0 0 0 1 0 0 0 1 1 1 1 1 1.3972, 0.9916 7 0 0 0 1 1 1 1 0 1 1 1 0 1 1 1 1 0 0 1.3808, 1.2444 8 0 0 0 1 1 1 1 1 0 0 0 1 1 1 0 0 0 1 0.9655, 1.1496 9 0 0 1 0 0 0 1 0 0 1 0 1 0 0 1 0 0 1 0.9655, 1.3977 10 0 0 1 0 0 0 1 1 1 1 1 0 0 0 1 0 0 0 1.3069, 1.0581 11 0 0 1 0 0 1 0 0 0 0 0 0 0 1 1 0 1 1 0.9909, 1.1499 12 0 0 1 0 1 0 0 0 1 0 1 0 0 1 0 0 0 1 1.2443, 1.3987 13 0 0 1 1 0 1 0 1 0 1 1 1 0 0 0 1 1 0 1.3985, 1.1795 14 0 0 1 1 0 1 1 0 0 0 0 0 1 0 1 0 0 0 1.1450, 1.3970 15 0 1 0 0 0 0 0 0 0 1 1 0 1 1 0 0 1 0 1.3798, 1.0231 16 0 1 0 1 0 1 1 0 0 0 1 1 1 1 0 0 0 1 0.9637, 1.3795 17 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 0 0 1 0.9646, 0.9907 18 0 1 1 0 0 0 1 1 1 1 0 0 0 1 0 1 0 1 1.0239, 1.1808 19 0 1 1 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 1.0213, 1.0231 20 0 1 1 1 1 1 0 1 1 1 0 0 0 0 0 1 1 1 1.3056, 1.2438 21 1 0 0 1 0 0 0 1 1 1 0 0 0 1 0 0 1 0 1.3972, 0.9916 22 1 0 1 0 1 0 0 0 1 1 1 0 0 1 1 1 0 0 1.3808, 1.2444 23 1 0 1 0 1 1 0 0 0 0 1 0 0 0 0 1 1 0 0.9655, 1.1496 24 1 0 1 1 0 0 1 0 0 1 0 0 0 0 0 0 0 1 0.9655, 1.3977 25 1 0 1 1 1 0 1 1 0 1 0 1 1 1 0 1 0 1 1.3069, 1.0581 26 1 0 1 1 1 1 1 0 0 0 1 0 0 0 1 1 1 1 0.9909, 1.1499 27 1 1 0 0 0 0 0 1 1 1 1 0 1 1 1 0 1 1 1.2443, 1.3987 28 1 1 1 0 0 0 0 1 1 1 0 0 1 0 1 0 1 0 1.3985, 1.1795 29 1 1 1 0 1 1 1 0 1 1 1 1 0 0 1 0 0 1 1.1450, 1.3970

Table D below shows base sequences of length 24 generated based on Scheme 1.

TABLE D Index sequence PAPR 0 0 0 0 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 0 0 0 0 1 1.5926, 1.5926 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 1.1500, 1.4099 2 0 0 0 0 1 0 0 0 0 1 1 0 0 0 1 1 1 0 1 0 1 0 1 1 1.6543, 1.6499 3 0 0 1 0 0 1 0 0 1 1 0 1 0 0 0 1 0 1 1 0 0 0 0 0 1.1476, 1.6542 4 0 0 1 0 0 1 0 0 1 0 0 1 0 1 0 1 1 1 0 1 0 0 0 1 1.6543, 1.4091 5 0 0 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 1.5912, 1.1500 6 0 0 1 0 1 1 0 0 0 0 0 0 0 1 0 0 1 0 0 1 1 0 1 0 1.6542, 1.4099 7 0 0 1 1 1 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 0 0 1 0 1.5926, 1.1476 8 0 0 1 0 1 1 1 0 1 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 1.5926, 1.1500 9 1 0 0 1 0 0 0 0 0 0 0 1 1 0 1 0 0 0 1 0 1 1 0 0 1.6543, 1.5926 10 1 0 0 0 0 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 0 0 0 1.4106, 1.4091 11 1 0 0 0 0 0 0 0 1 1 0 1 0 0 0 1 0 1 1 0 0 1 0 0 1.6543, 1.5926 12 1 0 0 1 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 0 0 1 0 0 1.1476, 1.5918 13 1 0 0 0 0 0 0 0 1 0 0 1 0 0 1 1 0 1 0 0 0 1 0 1 1.5912, 1.6543 14 1 0 0 0 1 1 1 0 0 0 1 1 1 1 1 1 0 1 1 1 1 0 1 1 1.1476, 1.6543 15 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1 0 0 1 1 1 1 0 1 1 1.5926, 1.5926 16 1 0 0 0 1 1 1 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 1.1500, 1.4099 17 1 1 0 0 1 0 1 1 1 0 1 0 0 1 1 0 1 1 0 1 1 1 1 1 1.6543, 1.6499 18 1 0 1 1 0 1 1 1 0 1 0 0 0 1 0 1 0 1 1 0 1 1 0 1 1.1476, 1.6542 19 1 1 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 1 1 0 0 0 1.6543, 1.4091 20 1 1 1 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 1 0 1 0 1 0 1.5912, 1.1500 21 1 0 1 0 0 0 1 0 1 1 0 0 1 0 0 1 0 0 0 0 0 0 0 1 1.6542, 1.4099 22 1 0 1 1 0 1 1 0 1 1 0 1 1 1 0 1 0 0 0 1 0 1 0 1 1.5926, 1.1476 23 1 1 1 0 0 0 1 1 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1.5926, 1.1500 24 1 0 1 0 0 0 1 1 1 0 0 1 1 1 1 0 1 1 1 1 0 0 1 0 1.6543, 1.5926 25 1 0 1 0 0 0 1 0 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 1 1.4106, 1.4091 26 1 1 1 0 0 0 1 1 1 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1.6543, 1.5926 27 1 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1.1476, 1.5918 28 1 1 1 0 0 1 1 1 1 0 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1.5912, 1.6543 29 1 0 1 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 0 1 1 1.1476, 1.6543

Table E below shows base sequences of length 24 generated based on Scheme 2.

TABLE E Index sequence PAPR 0 0 0 0 0 0 0 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1 1 1 1.0125, 1.0233 1 0 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 1 0 1.2587, 1.5191 2 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 1 0 0 0 0 0 1 1 0 1.2582, 1.5141 3 0 0 0 0 1 0 0 0 0 1 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1.1758, 1.2581 4 0 0 0 0 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1 1 1 0 0 1.0129, 1.0244 5 0 0 0 0 1 0 0 1 1 0 1 0 0 0 0 0 1 1 0 0 0 1 0 1 1.7849, 1.5275 6 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 1 0 0 0 1.2582, 1.5141 7 0 0 0 0 1 0 0 1 1 1 1 1 1 0 0 1 0 1 0 1 0 0 1 1 1.0238, 1.1638 8 0 0 0 0 1 1 0 0 1 0 1 1 1 0 0 1 0 1 0 1 1 0 0 0 1.0243, 1.1660 9 0 0 0 0 1 1 0 0 1 0 1 0 1 0 0 1 1 1 1 1 1 0 0 1 1.0238, 1.1638 10 0 0 0 0 1 0 0 0 1 1 1 0 1 0 1 1 0 1 1 0 1 1 1 0 1.3149, 1.5081 11 0 0 0 0 1 0 1 1 0 0 0 1 0 1 1 1 0 1 1 0 0 0 0 1 1.1758, 1.2581 12 0 0 0 0 1 1 1 0 0 1 0 1 0 1 1 1 0 0 1 0 0 1 0 0 1.0125, 1.0233 13 0 0 0 0 1 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 0 1 1 0 1.5288, 1.7809 14 0 0 0 0 1 1 1 0 0 0 1 0 0 1 0 1 0 0 0 1 0 0 1 0 1.3112, 1.5049 15 0 0 0 0 1 0 1 0 0 0 1 1 0 0 0 0 0 1 0 1 1 0 0 1 1.7849, 1.5275 16 0 0 0 0 1 1 1 0 1 1 0 1 1 0 1 0 1 1 1 0 0 0 1 0 1.5049, 1.3112 17 0 0 0 0 1 0 1 1 1 0 1 0 0 1 1 1 0 1 1 1 1 0 1 1 1.1758, 1.2581 18 0 0 0 0 1 1 1 0 1 0 1 1 0 0 1 0 1 0 0 1 1 0 0 0 1.5141, 1.2582 19 0 0 1 0 0 0 0 1 0 1 0 0 0 1 1 0 0 0 0 0 1 0 1 1 1.5275, 1.7849 20 0 0 1 0 0 1 0 1 0 0 0 1 0 0 1 0 0 0 0 0 1 1 1 0 1.3137, 1.5059 21 0 0 1 0 0 1 0 0 0 1 0 1 0 0 1 0 0 0 1 1 1 0 0 0 1.5049, 1.3112 22 0 0 1 0 0 1 0 1 0 1 0 0 1 1 0 0 0 0 0 1 1 0 0 0 1.2590, 1.5194 23 0 0 1 0 0 1 0 0 0 0 0 1 1 1 0 0 0 1 0 0 1 0 1 0 1.5059, 1.3137 24 0 0 1 0 0 1 0 1 0 0 0 1 1 1 0 1 1 1 1 1 0 0 0 1 1.5081, 1.3149 25 0 0 1 0 0 1 0 0 0 0 0 0 1 1 1 0 0 1 0 1 0 1 1 1 1.0129. 1.0244 26 0 0 1 0 0 1 0 1 0 1 1 1 0 0 0 1 1 0 1 1 1 1 1 1 1.0244, 1.0129 27 0 0 1 0 0 0 0 1 0 1 1 0 0 0 1 0 1 1 1 0 1 1 0 0 1.2581, 1.1758 28 0 0 1 0 0 0 0 0 0 1 1 0 1 1 0 1 0 1 0 0 0 1 1 1 1.0129, 1.0244 29 0 0 1 0 0 1 0 0 0 1 1 1 1 1 0 1 1 1 0 0 0 1 0 1 1.3112, 1.5049

Due to a short length, binary sequence with length 6 may not provide 30 candidates with desired properties. In certain configurations, as described supra, for DMRS sequence of length 6, the modulation component 714 employs an 8-BPSK modulation. In certain configurations, based on the indication from the base station 702, the modulation component 714 generates modulation symbols 744. The modulation symbols 744 may be represented as

s _(u)(n)=e ^(jϕ(n)π/8)

The values of ϕ(n) in each base sequence are listed in the below Table F and Table G.

TABLE F u ϕ(0), . . . , ϕ(5) PAPR (dB)  0 1 3 1 7 −3 −7 2.0214  1 1 3 1 −5 5 −7 1.9297  2 1 3 −3 7 5 −7 1.9507  3 1 5 3 −3 7 −7 1.9507  4 1 5 −1 −7 7 −7 1.9298  5 1 −3 1 −3 1 −3 1.8257  6 1 −3 3 −7 7 −7 2.0214  7* 1 −3 −7 −3 1 5 0.7838  8* 1 −3 −7 −3 1 −3 1.5331  9* 1 −3 −7 −3 −7 −3 1.5333 10 1 −1 1 5 −5 7 1.9143 11 1 −1 1 −5 7 −3 1.9943 12 1 −1 3 7 1 5 1.6125 13 1 −1 3 7 1 −3 1.8358  14* 1 −1 3 7 3 7 1.4624 15 1 −1 3 7 3 −3 1.4418 16 1 −1 3 7 −5 7 1.9852 17 1 −1 3 −7 5 −1 1.9942 18 1 −1 3 −3 1 5 1.7817 19 1 −1 3 −3 1 −3 1.7821 20 1 −1 3 −3 −7 −3 1.4418 21 1 −1 3 −1 3 7 1.6341 22 1 −1 3 −1 3 −3 1.7821 23 1 −1 3 −1 −7 −3 1.8359 24 1 −1 −7 5 −7 −3 1.9853 25 1 −1 −7 5 −5 −1 1.9144 26 1 −1 −7 −3 1 −3 1.6341  27* 1 −1 −7 −3 −7 −3 1.4624 28 1 −1 −5 −1 3 −3 1.7817 29 1 −1 −5 −1 −7 −3 1.6126

TABLE G u ϕ(0), . . . , ϕ(5) PAPR (dB)  0 1 3 8 3 −2 −4 1.9053  1 1 3 8 3 −1 −4 1.9468  2 1 4 1 5 0 −4 1.8828  3* 1 4 8 −3 −6 5 1.3821  4 1 4 −7 4 1 −3 1.9658  5 1 5 0 4 0 −3 1.5759  6 1 5 1 5 −7 5 1.5331  7 1 5 3 6 1 −4 1.5936  8 1 5 8 4 −1 −4 1.3821  9* 1 5 −7 6 2 6 1.5758 10 1 5 −6 5 1 4 1.7337 11 1 5 −6 6 1 −2 1.4665 12 1 5 −6 6 2 5 1.8650 13 1 5 −6 8 3 −2 1.3993 14 1 6 8 3 −1 −4 1.7834 15 1 6 −7 5 1 −3 1.9500 16 1 6 −7 7 2 −3 1.7900 17 1 6 −6 6 2 −2 1.9503  18* 1 6 −6 6 −7 6 1.9287 19 1 −4 7 −6 8 −4 1.5937 20 1 −4 8 5 −7 −4 1.9744  21* 1 −4 −7 −4 8 −4 1.9287 22 1 −4 −6 5 8 −4 1.9375  23* 1 −3 8 5 −6 −2 1.3821 24 1 −3 −7 5 −7 −3 0.7839 25 1 −3 −6 5 −6 −3 1.9658 26 1 −2 −7 5 −6 −1 1.9045 27 1 −1 −6 5 7 −4 1.5718 28 1 −1 −6 5 −7 −4 1.5310 29 1 −1 −6 5 −6 −3 1.9541

Sequences marked with * are a subset with better auto-/cross-correlation and PAPR.

The sequences in Table F and Table G are normalized to have same starting phase (i.e., e{circumflex over ( )}(jπ/8)). Because PAPR, circular auto-correlation and cross-correlation properties are invariant with respect to constant phase rotation or circular shift, the actual sequences can be derived by applying such operations to the sequences in Table F and Table G.

In particular, the DMRS sequences listed in the below Table H can be derived from a sequence listed in Table F or Table G.

TABLE H u ϕ(0) . . . ϕ(5) 0 −1 −7 −3 −5 −1 3 1 −1 3 1 5 −1 −5 2 −7 −3 −7 5 −7 −3 3 −7 −3 −7 −3 7 −5 4 −7 −3 1 −5 −1 −5 5 −3 7 −5 −1 −5 −1 6 5 −7 7 1 5 1 7 1 5 1 5 3 7 8 1 −3 1 −5 −1 3

Further, in Scheme 4, when the length of a desired base DMRS sequence is N (e.g., 24), to generate a DMRS sequence for port 2, the DMRS sequence component 712 initially generates a base DMRS sequence having a length of N/2 (e.g., 12). The DMRS sequence of length N/2 is sent to the modulation component 714 to generate a set of symbols (e.g., N/2). The set of symbols is repeated to generate a duplicate set of symbols (e.g., total N symbols). The below time domain orthogonal cover code (TD-OCC) is applied to the symbols.

$\left\lbrack {W_{N\text{/}2},{- W_{N\text{/}2}}} \right\rbrack,{{{where}\mspace{14mu} {W_{N\text{/}2}(n)}} = \left( {- 1} \right)^{n}},{n = 0},\ldots \mspace{14mu},{\frac{N}{2} - 1.}$

For example, the TD-OCC may be [1, −1. 1, −1. 1, −1. 1, −1. 1, −1. 1, −1. −1. 1, −1, 1, −1. 1, −1. 1, −1. 1, −1. 1]. Subsequently, the symbols applied with TD-OCC are sent to the DFT-s-OFDM component 718.

In Scheme 5, to generate a DMRS sequence of length N for port 2, the DMRS sequence component 712 initially generates a base DMRS sequence of N (e.g., 12). The DMRS sequence of length N is sent to the modulation component 714 to generate a set of symbols (e.g., N). The below TD-OCC is applied to the symbols.

$\left\lbrack {e^{j\; \frac{2\; \pi \; n}{N}} \cdot {W_{N}(n)}} \right\rbrack_{{n = 0},\ldots,{N - 1}},{{{where}\mspace{14mu} {W_{N}(n)}} = \left( {- 1} \right)^{n}},{n = 0},\ldots \mspace{14mu},{N - 1.}$

FIG. 8 is a flow chart 800 of a method (process) for generating and transmitting a DMRS sequence. The method may be performed by a first UE (e.g., the UE 704, the apparatus 902, and the apparatus 902′).

At operation 802, the UE receives an indication for transmitting a particular demodulation reference signal (DMRS) sequence in an uplink transmission. The particular DMRS sequence is time domain based. At operation 804, the UE generates the particular DMRS sequence. At operation 806, the UE modulates the particular DMRS sequence to obtain a set of symbols. At operation 808, the UE maps a plurality of symbols of the set of symbols to a plurality of subcarriers. At operation 810, the UE transmits the plurality of symbols on the plurality of subcarriers.

In certain configurations, the modulating is based on π/2-Binary Phase-Shift Keying (BPSK). In certain configurations, the particular DMRS sequence is one of 000100100010, 010001001000, and 101111011011. In certain configurations, the particular DMRS sequence is one of 000111000100011111, 010100011010000011, and 001010001010010001. In certain configurations, the particular DMRS sequence is one of 001001010001001000001110, 000010011010000011000101, 101000111001111011110010, and 001001000001110001001010.

In certain configurations, the modulating is based on 8-ary Phase-Shift Keying (8-PSK). In certain configurations, the set of symbols is based on one of:

-   -   [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(−j7π/8),         e^(−j3π/8)],     -   [e^(jπ/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8),         e^(−j3π/8)], and     -   [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(j3π/8),         e^(j7π/8)].

In certain configurations, the set of symbols is based on one of:

-   -   [e^(−jπ/8), e^(−j7π/8), e^(−j3π/8), e^(−j5π/8), e^(−j7π/8),         e^(j3π/8)],     -   [e^(−jπ/8), e^(j3π/8), e^(jπ/8), e^(j5π/8), e^(−jπ/8),         e^(−j5π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(j5π/8), e^(−j7π/8),         e^(−j3π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(−j3π/8), e^(j7π/8),         e^(−j5π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8),         e^(−j5π/8)],     -   [e^(−j3π/8), e^(j7π/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8),         e^(−jπ/8)],     -   [e^(j5π/8), e^(−j7π/8), e^(j7π/8), e^(jπ/8), e^(j5π/8),         e^(jπ/8)],     -   [e^(jπ/8), e^(j5π/8), e^(jπ/8), e^(j5π/8), e^(j3π/8),         e^(j7π/8)], and     -   [e^(jπ/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8),         e^(j3π/8)],

FIG. 9 is a conceptual data flow diagram 900 illustrating the data flow between different components/means in an exemplary apparatus 902. The apparatus 902 may be a UE. The apparatus 902 includes a reception component 904, a DMRS sequence generator 906, a modulation component 908, an OFDM component 909, and a transmission component 910.

The DMRS sequence generator 906 receives an indication from a base station 950 for transmitting a particular DMRS sequence in an uplink transmission. The particular DMRS sequence is time domain based. The DMRS sequence generator 906 generates the particular DMRS sequence. The modulation component 908 modulates the particular DMRS sequence to obtain a set of symbols. The OFDM component 909 maps a plurality of symbols of the set of symbols to a plurality of subcarriers. The transmission component 910 transmits the plurality of symbols on the plurality of subcarriers.

In certain configurations, the modulating is based on π/2-Binary Phase-Shift Keying (BPSK). In certain configurations, the particular DMRS sequence is one of 000100100010, 010001001000, and 101111011011. In certain configurations, the particular DMRS sequence is one of 000111000100011111, 010100011010000011, and 001010001010010001. In certain configurations, the particular DMRS sequence is one of 001001010001001000001110, 000010011010000011000101, 101000111001111011110010, and 001001000001110001001010.

In certain configurations, the modulation component 908 modulates the DMRS sequence based on 8-ary Phase-Shift Keying (8-PSK). In certain configurations, the set of symbols generated by the modulation component 908 is based on one of:

-   -   [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(−j7π/8),         e^(−j3π/8)],     -   [e^(jπ/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8),         e^(−j3π/8)], and     -   [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(j3π/8),         e^(j7π/8)].

In certain configurations, the set of symbols generated by the modulation component 908 is based on one of:

-   -   [e^(−jπ/8), e^(−j7π/8), e^(−j3π/8), e^(−j5π/8), e^(−j7π/8),         e^(j3π/8)],     -   [e^(−jπ/8), e^(j3π/8), e^(jπ/8), e^(j5π/8), e^(−jπ/8),         e^(−j5π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(j5π/8), e^(−j7π/8),         e^(−j3π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(−j3π/8), e^(j7π/8),         e^(−j5π/8)],     -   [e^(−j7π/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8),         e^(−j5π/8)],     -   [e^(−j3π/8), e^(j7π/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8),         e^(−jπ/8)],     -   [e^(j5π/8), e^(−j7π/8), e^(j7π/8), e^(jπ/8), e^(j5π/8),         e^(jπ/8)],     -   [e^(jπ/8), e^(j5π/8), e^(jπ/8), e^(j5π/8), e^(j3π/8),         e^(j7π/8)], and     -   [e^(jπ/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8),         e^(j3π/8)],

FIG. 10 is a diagram 1000 illustrating an example of a hardware implementation for an apparatus 902′ employing a processing system 1014. The apparatus 902′ may be a UE. The processing system 1014 may be implemented with a bus architecture, represented generally by a bus 1024. The bus 1024 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1014 and the overall design constraints. The bus 1024 links together various circuits including one or more processors and/or hardware components, represented by one or more processors 1004, the reception component 904, the DMRS sequence generator 906, the modulation component 908, the OFDM component 909, the transmission component 910, and a computer-readable medium/memory 1006. The bus 1024 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, etc.

The processing system 1014 may be coupled to a transceiver 1010, which may be one or more of the transceivers 354. The transceiver 1010 is coupled to one or more antennas 1020, which may be the communication antennas 352.

The transceiver 1010 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1010 receives a signal from the one or more antennas 1020, extracts information from the received signal, and provides the extracted information to the processing system 1014, specifically the reception component 904. In addition, the transceiver 1010 receives information from the processing system 1014, specifically the transmission component 910, and based on the received information, generates a signal to be applied to the one or more antennas 1020.

The processing system 1014 includes one or more processors 1004 coupled to a computer-readable medium/memory 1006. The one or more processors 1004 are responsible for general processing, including the execution of software stored on the computer-readable medium/memory 1006. The software, when executed by the one or more processors 1004, causes the processing system 1014 to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory 1006 may also be used for storing data that is manipulated by the one or more processors 1004 when executing software. The processing system 1014 further includes at least one of the reception component 904, the DMRS sequence generator 906, the modulation component 908, the OFDM component 909, and the transmission component 910. The components may be software components running in the one or more processors 1004, resident/stored in the computer readable medium/memory 1006, one or more hardware components coupled to the one or more processors 1004, or some combination thereof. The processing system 1014 may be a component of the UE 350 and may include the memory 360 and/or at least one of the TX processor 368, the RX processor 356, and the communication processor 359.

In one configuration, the apparatus 902/apparatus 902′ for wireless communication includes means for performing each of the operations of FIG. 8. The aforementioned means may be one or more of the aforementioned components of the apparatus 902 and/or the processing system 1014 of the apparatus 902′ configured to perform the functions recited by the aforementioned means.

As described supra, the processing system 1014 may include the TX Processor 368, the RX Processor 356, and the communication processor 359. As such, in one configuration, the aforementioned means may be the TX Processor 368, the RX Processor 356, and the communication processor 359 configured to perform the functions recited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in the processes/flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module,” “mechanism,” “element,” “device,” and the like may not be a substitute for the word “means.” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.” 

What is claimed is:
 1. A method of wireless communication of a user equipment (UE), comprising: receiving an indication for transmitting a particular demodulation reference signal (DMRS) sequence in an uplink transmission, the particular DMRS sequence being time domain based; generating the particular DMRS sequence; modulating the particular DMRS sequence to obtain a set of symbols; mapping a plurality of symbols of the set of symbols to a plurality of subcarriers; and transmitting the plurality of symbols on the plurality of subcarriers.
 2. The method of claim 1, wherein the modulating is based on π/2-Binary Phase-Shift Keying (BPSK).
 3. The method of claim 2, wherein the particular DMRS sequence is one of 000100100010, 010001001000, and
 101111011011. 4. The method of claim 2, wherein the particular DMRS sequence is one of 000111000100011111, 010100011010000011, and
 001010001010010001. 5. The method of claim 2, wherein the particular DMRS sequence is one of 001001010001001000001110, 000010011010000011000101, 101000111001111011110010, and
 001001000001110001001010. 6. The method of claim 1, wherein the modulating is based on 8-ary Phase-Shift Keying (8-PSK).
 7. The method of claim 6, wherein the set of symbols is based on one of: [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(−j7π/8), e^(−j3π/8)], [e^(jπ/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8), e^(−j3π/8)], and [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(j3π/8), e^(j7π/8)].
 8. The method of claim 6, wherein the set of symbols is based on one of: [e^(−jπ/8), e^(−j7π/8), e^(−j3π/8), e^(−j5π/8), e^(−j7π/8), e^(j3π/8)], [e^(−jπ/8), e^(j3π/8), e^(jπ/8), e^(j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(j5π/8), e^(−j7π/8), e^(−j3π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(−j3π/8), e^(j7π/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j3π/8), e^(j7π/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8)], [e^(j5π/8), e^(−j7π/8), e^(j7π/8), e^(jπ/8), e^(j5π/8), e^(jπ/8)], [e^(jπ/8), e^(j5π/8), e^(jπ/8), e^(j5π/8), e^(j3π/8), e^(j7π/8)], and [e^(jπ/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8)].
 9. An apparatus for wireless communication, the apparatus being a user equipment (UE), comprising: a memory; and at least one processor coupled to the memory and configured to: receive an indication for transmitting a particular demodulation reference signal (DMRS) sequence in an uplink transmission, the particular DMRS sequence being time domain based; generate the particular DMRS sequence; modulate the particular DMRS sequence to obtain a set of symbols; map a plurality of symbols of the set of symbols to a plurality of subcarriers; and transmit the plurality of symbols on the plurality of subcarriers.
 10. The apparatus of claim 9, wherein the modulating is based on π/2-Binary Phase-Shift Keying (BPSK).
 11. The apparatus of claim 10, wherein the particular DMRS sequence is one of 000100100010, 010001001000, and
 101111011011. 12. The apparatus of claim 10, wherein the particular DMRS sequence is one of 000111000100011111, 010100011010000011, and
 001010001010010001. 13. The apparatus of claim 10, wherein the particular DMRS sequence is one of 001001010001001000001110, 000010011010000011000101, 101000111001111011110010, and
 001001000001110001001010. 14. The apparatus of claim 9, wherein the modulating is based on 8-ary Phase-Shift Keying (8-PSK).
 15. The apparatus of claim 14, wherein the set of symbols is based on one of: [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(−j7π/8), e^(−j3π/8)], [e^(jπ/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8), e^(−j3π/8)], and [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(j3π/8), e^(j7π/8)].
 16. The apparatus of claim 14, wherein the set of symbols is based on one of: [e^(−jπ/8), e^(−j7π/8), e^(−j3π/8), e^(−j5π/8), e^(−j7π/8), e^(j3π/8)], [e^(−jπ/8), e^(j3π/8), e^(jπ/8), e^(j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(j5π/8), e^(−j7π/8), e^(−j3π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(−j3π/8), e^(j7π/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j3π/8), e^(j7π/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8)], [e^(j5π/8), e^(−j7π/8), e^(j7π/8), e^(jπ/8), e^(j5π/8), e^(jπ/8)], [e^(jπ/8), e^(j5π/8), e^(jπ/8), e^(j5π/8), e^(j3π/8), e^(j7π/8)], and [e^(jπ/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8)].
 17. A computer-readable medium storing computer executable code for wireless communication of a user equipment (UE), comprising code to: receive an indication for transmitting a particular demodulation reference signal (DMRS) sequence in an uplink transmission, the particular DMRS sequence being time domain based; generate the particular DMRS sequence; modulate the particular DMRS sequence to obtain a set of symbols; map a plurality of symbols of the set of symbols to a plurality of subcarriers; and transmit the plurality of symbols on the plurality of subcarriers.
 18. The computer-readable medium of claim 17, wherein the modulating is based on π/2-Binary Phase-Shift Keying (BPSK).
 19. The computer-readable medium of claim 18, wherein the particular DMRS sequence is one of 000100100010, 010001001000, and
 101111011011. 20. The computer-readable medium of claim 18, wherein the particular DMRS sequence is one of 000111000100011111, 010100011010000011, and
 001010001010010001. 21. The computer-readable medium of claim 18, wherein the particular DMRS sequence is one of 001001010001001000001110, 000010011010000011000101, 101000111001111011110010, and
 001001000001110001001010. 22. The computer-readable medium of claim 17, wherein the modulating is based on 8-ary Phase-Shift Keying (8-PSK).
 23. The computer-readable medium of claim 22, wherein the set of symbols is based on one of: [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(−j7π/8), e^(−j3π/8)], [e^(jπ/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8), e^(−j3π/8)], and [e^(jπ/8), e^(−jπ/8), e^(j3π/8), e^(−jπ/8), e^(j3π/8), e^(j7π/8)].
 24. The computer-readable medium of claim 22, wherein the set of symbols is based on one of: [e^(−jπ/8), e^(−j7π/8), e^(−j3π/8), e^(−j5π/8), e^(−j7π/8), e^(j3π/8)], [e^(−jπ/8), e^(j3π/8), e^(jπ/8), e^(j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(j5π/8), e^(−j7π/8), e^(−j3π/8)], [e^(−j7π/8), e^(−j3π/8), e^(−j7π/8), e^(−j3π/8), e^(j7π/8), e^(−j5π/8)], [e^(−j7π/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8)], [e^(−j3π/8), e^(j7π/8), e^(−j5π/8), e^(−jπ/8), e^(−j5π/8), e^(−jπ/8)], [e^(j5π/8), e^(−j7π/8), e^(j7π/8), e^(jπ/8), e^(j5π/8), e^(jπ/8)], [e^(jπ/8), e^(j5π/8), e^(jπ/8), e^(j5π/8), e^(j3π/8), e^(j7π/8)], and [e^(jπ/8), e^(−j3π/8), e^(jπ/8), e^(−j5π/8), e^(−jπ/8), e^(j3π/8)]. 